Recovery of solvent from hydrocarbon oils



All@ 1, 1939. E. R.v BRowNscoMBE ET AL 2,167,632

RECOVERY 0F SOLVENT FROM HYDROCARBON OILS Filed July 18, 1936 Patented ug. 1, 1939 UNE'EED STATES FTENT OFFHQE RECOVERY OF SOLVENT FROM HYDROCARBON OILS Pennsylvania Application July 18, 1936, Serial No. 91,342

11 Claims.

The present invention relates to the recovery of solvents from hydrocarbon oils, and relates more particularly to the separation and recovery of solvents such as the nitrate-d aromatic hydrocarbons, for example, nitrobenzene, nitrotoluene and the like, from oils which have been selectively extracted with such solvents.

A further object of this invention is the recovery of solvents, such as the nitrated aromatic hydrocarbons, from oil, whereby vaporization or distillation of the solvent is obviated or at least reduced to a minimum.

A further object of this invention is the recovery of nitrated aromatic hydrocarbons, and particularly nitrobenzene, from oils which have been selectively extracted with same, by means of a second solvent which at ordinary temperatures is relatively immiscible with oil and nitrobenzene, and which, at elevated temperatures, possesses substantial solvent power for nitrobenzene but not for oil.

One of the major expenses incident to solvent extraction of hydrocarbon oils, and particularly petroleum lubricating oils, is the distillation of the solvent, most of which is present in the extract or naphthenic oil phase. In the recovery of solvents by distillation, the heat employed in vaporizing the solvent is seldom, if ever, recovered. However, in accordance with the present invention, heat losses are reduced to `a minimum, since substantially all of the heating and cooling steps involve the handling of liquids without vaporization, and heat exchange may be employed with high eiiiciency.

Briefly, the present invention resides in an improved method of recovering selective solvents such as the nitrated aromatic hydrocarbons, for example, nitrobenzene, nitrotoluene and the like, from hydrocarbon oil which has been selectively extracted with the same. Hydrocarbon oils, and particularly lubricating oil stocks, are subjected to treatment with a ntrated aromatic hydrocarbon, such as nitrobenzene, to form a rainate phase comprising the more parainic portion of the oil together with a minor quantity of solvent, and an extract phase comprising the more naphthenic portion of the oil in solution in the major portion of the solvent. The raffinate and extract phases are separated from one another, and either one or both of the phases are subjected to treatment with a second solvent for the removal of the nitrobenzene therefrom.

In the case of the recovery of the nitrated aromatic hydrocarbon, for example, nitrobenzene, the oil-nitrobenzene mixture is brought into contact (Cl. Zim-645) with a second solvent, which at ordinary temperature, is relatively immiscible with the nitrobenzene and with oil, but which at elevated temperatures is substantially miscible with the nitrobenzene but not with oil. Among the suitable secondary solvents are the hydroxy compounds, preferably the aliphatic hydroxy compounds such as methyl alcohol, ethyl alcohol, propyl alcohol or mixtures of these alcohols with Water, and the polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol and Water, and the like. The contacting of the oil-nitrobenzene mixture with the second solvent, e. g., the hydroxy compound, is carried. on at temperatures of the order of about 250 F. to about 400 F., under elevated pressure suflicient to maintain the second solvent in the liquid phase. At such temperatures the nitrobenzene is extracted from the oil to a substantial extent and a separate phase is formed comprising the hydroxy compound, the major portion of the nitrobenzene, and a small amount of oil. The remaining phase comprises essentially oil containing a small percentage of nitrobenzene and hydroxy compound. Th e phases are separated from one another, for example, by decantation, and that phase comprising the hydroxy compound and the major portion of the nitrobenzene is cooled, preferably to a temperature of the order of about 150 F. to 60 F., or less, whereupon the bulk of the nitrobenzene separates from the second solvent, e. g., the hydroxy compound. Each solvent may be recirculated without further treatment, i. e., the nitrobenzene to the primary extraction system and the hydroxy compound to the solvent recovery system.

As a further illustration of our process of solvent recovery, an extract solution from a nitrobenzene solvent extraction system, consisting of about 25 parts of naphthenic oil in solution in 75 parts of nitrobenzene, was admixed with 200 parts of ethylene glycol. At a temperature of about 80 F., very little nitrobenzene, and no measurable quantity of oil is dissolved in the ethylene glycol. When, however, the mixture is heated to about 320 F., a very large proportion of the nitrobenzene is dissolved by the ethylene glycol, leaving substantially all the oil, with a small amount of nitrobenzene, as the second phase. The two phases may be separated and the small quantity of nitrobenzene may be removed from the oil phase, for example, by steam stripping. The remaining phase, at about 320 F. comprises ethylene glycol, nitrobenzene and a very small proportion of oil. This solution, upon being returned to the solvent recovery system for theV separation of nitrobenzene from additional quantities of nitrobenzene-oil mixtures.

In order to more clearly describe our invention, Y

reference is had to the accompanying drawing which illustrates'diagrammatically a method of treating hydrocarbon oil with Va selective solvent such as nitrobenzene and the recovery of the nitrobenzene for reusev in accordance with the procedure of our invention.

Referring to the drawing, a Vselective solvent such as nitrobenzene is introduced into the upper section ofthe extraction tower I by means of valve-'controlled pipe `2 anddistributing head 3, and a hydrocarbon oil, for example, a lubricating oil stock, is introduced into the lower section of tower I through valve-controlled pipe 5y and distributing head 6. The nitrobenzene, being of greater specific gravity than the oil, descends in countercurrent contact with the oil and the more naphthenic components-of the oil pass into solution in the solvent, thus forming the extract phase, while the. undissolved oil, containing a small portion of solvent and constituting the raffinate phase, is withdrawn from the top of the tower by means of valve-controlled pipe 'I. The extract phase, comprising the bulk of the solvent and containing dissolved naphthenic components, is withdrawn from the bottom of the tower I through pipe 8 and is pumped by pump 9 through pipe I0 and heat exchanger II wherein the temperature of the extract solution is Vraised to about 350 F. The heated solution from exchanger II is introduced into the upper section of a second contacting tower I2 by means of valve-controlled pipeV I3 and distributing head I4, and a second Y solvent, for example, methanol-50% water,

supplied through valve-controlled pipe I5, is pumped by pump I6 through heat-exchanger coil I'I and heater I8, heated to about 350 F., and passed through pipe I9 and distributing head 20 'into the lower section of tower I2. Sufficient pressure is maintained within the system that the oil and solvents remain substantially in the liquid phase throughout the recovery operation. Countercurrent contacting of the heated extract 'and the methanol-water is effected in tower I2, the major portion of the nitrobenzene being dissolved from the extract by the methanol-water. The final extract oil, containing a relatively small quantity of nitrobenzene and methanol-water, is withdrawn from the bottom of tower I2 by means of valve-controlled pipe 2I and may be passed to a stripping still (not shown) wherein residual nitrobenzene and traces of methanol-Water may be removed.

The second solvent, i. e., methanol-Water, having dissolved the major portion of the nitrobenzene and a small amount of oil Vfrom the heated extract, is withdrawn from the top of tower I2 and passed through valve-controlledv pipe 22 into heat-exchanger shell 23. Herein, heat-exchange with the methanol-water in coil II is eifected, the methanol-water-nitrobenzene solution in shell 23 being cooled to a temperature of about 100 F., the methanol-water inthe coil I1 absorbing the heat. The methanol-waternitrobenzene mixture, at about 100 F., is passed from the exchanger shell 23 into separator 24 by means of pipe 25. The lowering of the temperature of'the methanol-water-nitrobenzene mixture from about 350 F. to about 100 F. causes the formation of two phases, one comprising methanol-water containing a small percentage of nitrobenzene and oil, and the other, nitrobenzene and a small amount of methanol-water and oil. The two phases .resulting from the cooling step are permitted Yto stratify into layers in separator 24, the methanol-Water being withdrawn from the upper section of the separator by means of Valve-controlled pipe 26 and recirculated to the recovery system by means of pump I6. The nitrobenzene containing a small amount of methanolwater and oil is withdrawn from the lower section of separator 24 through pipe 2'! and recirculated by pump 28 through valve-controlled pipe 29 to the upper section of the extraction tower I In the operation of our solvent extraction and recovery system, it has been found that the equilibrium between the extraction solvent, for example, nitrobenzene, and the second or recovery solvent, for example, methanol-water, is practically constant. Or, in other words, there is substantially no build-up of methanol-Water in the nitrobenzene in the primary extraction system, nor is there any build-up of nitrobenzene in methanol-water in the recovery system. In instances where the content of naphthenic oil in the recovered nitrobenezene may increase, it is desirable to remove at least a portion of such recovered solvent from the system, for example, by means of valve-controlled pipe 30, and subject the solvent to distillation to separate same from the oil. Such solvent, substantially free of oil, Vmay be re-introduced into the primary extraction system through valve-controlled pipe 2.

While we have described our solvent recovery step with particular reference to the separation of solvent from the extract or naphthenic oil phase, we may also subject the raffinate or parafiinic oil phase to a similar treatment for the recovery of solvent therefrom. Furthermore, We have found that in lieu of methanol-water, we may employ ethyl alcohol, propyl alcohol, ethylene glycol, propylene glycol, butylene glycol, and diethylene glycol or mixtures of the alcohols with oneV another and/or with water. In the utilization of methyl and ethyl alcohol, it is generally desirable to dilute the alcoholY with water to give, for example, mixtures containing 50% of alcohol and,50% of water, the water in the alcohol serving to decrease the miscibility of the mixture with hydrocarbon oil. The dilution need not be in the ratio of 1:71, since other proportions may be employed, depending upon the alcohol, and the temperature and pressure conditions in the-recovery system. The primary oil extraction system and/or the solvent recovery system may be of the single stage continuous countercurrent type described with reference to the drawing, or may be of the multi-stage countercurrent type or simply of the batch type. However, it has been found that the countercurrent systems are preferable, particularly from the view point of efciency and economy.

The following example is typical of the results which may be obtained in accordance with our invention: Y

100 bbls. per hour of an East Texas lubricating oil distillate having a Saybolt Universal viscosity of V110 seconds at 210 F., an A. P. I. gravity of 21.3, and a viscosity-gravity constant of 0.854, 75

Was extracted in a 3-stage batch countercurrent extraction system at 68 F. with recoverednitrobenzene charged at a rate of 190 bbls. per hour. lThe recovered nitrobenzene solvent was composed of 88.5% of nitrobenzene, 7.9% of ethylene glycol and 3.6% of oil. There was produced a yield or 57.2 bbls. per hour of rainate phase consisting of 85.6% rafnate oil, 14% nitrobenzene and 0.4 ethylene glycol. Upon removal of the solvents from the rainate phase, for example, by distillation and/or steam stripping, there resulted a yield of 49 bbls. -per hour of rainate oil having a Saybolt Universal viscosity of 83 seconds at 210 F., an A. P. I. gravity of 27.3, and a viscosity-gravity constant of 0.814. The extract phase Withdrawn from the primary extraction system amounted. to 283 bbls. per hour and comprised a solution of 68.7% nitrobenzene, 6.4% ethylene glycol and 24.9% naphthenic oil.' This extract phase Was charged at the rate of 233 bbls. per hour to a S-stage batch countercurrent extraction system and contacted at about 340 F. with a second or recovery solvent charged at a rate of 327 bbls. per hour. The second or recovery solvent was composed of 87 .8% of ethylene glycol and 12.2% of nitrobenzene. There resulted from this contacting operation a yield of bbs. per hour of a naphthenic oil solution consisting of 68% oil, 26.6%V nitrobenzene and 5.4% ethylene glycol, from which was recovered, after removal of the solvent by distillation, a naphthenic oil fraction amounting to 51 bbls. per hour and having Saybolt Universal viscosity of 168 seconds at 210 F., an A. P. I. gravity of 16.4, and a viscosity-gravity constant of 0.887. The other phase resulting from this contacting operation amounted to 485 bbls. per hour and comprised a solution of 37.1% of nitrobenzene, 61.5% ethylene glycol and 1.4% oil. This solution was cooled to about F. and permitted to settle, whereupon there was formed a two-layer system, one phase consisting of 87.8% of ethylene glycol and 12.2% of nitrcbenzene, which phase was recirculated as the second solvent to the solvent recovery system at the rate of 327 bbls. per hour. The remaining phase, consisting of 88.6% nitrobenzene, 6.6% ethylene glycol and 4.8% oil, and amounting to 158 bbls. per hour, was added to the small quantity of solvents stripped from the raffinate and extract oil fractions, and the composite solvent, predominantly nitrobenzene, Was recirculated to the primary oil extraction system to extract additional quantities of untreated oil.

1t will be seen that, in accordance with our invention, it is possible to recover the major portion of the primary solvent, e. g., nitrobenzene,

from oil fractions substantially entirely in the liquid phase, thus eliminating, for the most part, the necessity for distillation. Furthermore, since the recovery of solvent is accomplished in the liquid phase, heat exchange in the heating and cooling steps may be employed with high eiciency.

Herein, and in the appended claims, the term nitrated aromatic hydrocarbon is to be understood to comprehend nitrobenzene, nitrotoluene, nitronaphthalene and the like or mixtures thereof. Also, the term aliphatic alcohol is to be understood to comprehend methyl alcohol, ethyl alcohol, propyl alcohol or mixtures of same with one another or With Water, as Well as the polyhydric alcohols such as ethylene glycol, propylene glycol, butylene glycol, diethyline glycol, and mixtures thereof with one another and/or with Water and/or the monohydric alcohols.

What We' claim is:

1. The. method of recovering a nitrated aromatic hydrocarbon from admixture with hydrocarbon oil, which comprises contacting the nitrated aromatic hydrocarbon and oil, at a temperature o1" from about 250 F. to about 400 F., with a solvent, which at temperatures oi from about 250 F. to 400 F. has substantial solvent power for the nitrated aromatic hydrocarbon but not for oil, and which at temperatures less than about 15 F. has relatively little solvent power for the nitrated aromatic hydrocarbon and for effectincr separation of the oil constituents from the nitrated aromatic hydrocarbon While maintaining the mixture at said elevated temperature, removing separated oil, and cooling the remaining mixtureY to separate and. recover the nitrated aromatic hydrocarbon.

2. The method of recovering a nitrated laromatic hydrocarbon from` admixture with hydrocarbon oil, which comprises contacting the niaromatic hydrocarbon and oil, at a temperature of from about 250 F. to about 400 F., with a solvent, Which at temperatures of from about 250 F. to 400 F. has substantial solvent power for the nitrated aromatic hydrocarbon but not for oil, and which at temperatures less than ascut 150 F. has relatively little solvent power for the nitrated aromatic hydrocarbon and for oil, eflecting separation of the oil constituents from the nitrated aromatic hydrocarbon While maintaining the mixture at said elevated temperature, removing separated oil, and cooling the remaining mixture to a temperature of less than substantially 150 F. to separate and recover the .'f.

nitrated aromatic hydrocarbon.

3. The method of recovering a nitrated aromatic hydrocarbon from admixture with hydrocarbon oil, which comprises contacting the nitrated aromatic hydrocarbon and oil with an aliphatic alcohol at a temperature of from about 250 F. to about 400 F., effecting separation of the oil constituents from the nitrated aromatic hydrocarbon while maintaining the mixture at substantially such temperature, removing the separated oil, and cooling the remaining mixture to separate and recover the nitrated aromatic hydrocarbon.

4. The method of recovering a nitrated aromatic hydrocarbon from a-dmixture with hydrocarbon oil, which comprises contacting the nitrated aromatic hydrocarbon and oil with an aliphatic alcohol at a temperature of from about 250 F. to about 400 F., effecting separation of the oil constituents from the nitrated aromatic hydrocarbon While maintaining the mixture at substantially such temperature, removing the separated oil, and cooling the remaining mixture to a temperature of less than substantially 150 F. to separate and recover the nitrated aromatic hydrocarbon.

5. The method of recovering a nitrated hy:

gli

matic hydrocarbon from admixture With hydro- 75 carbon oil, which comprises contacting theni-V trated aromatic hydrocarbon and oil with a diluted aliphatic alcoholat a temperature of from about 250 F. to about 400 F., effecting separation of the oil constituents from the nitrated aromatic hydrocarbon while maintaining the mixture at Vsubstantially such temperature, removing theV separated oil, and cooling the remaining mixture to a temperature of less than substantially 150 F. to separate and recover the nitrated aromatic hydrocarbon.

'7. The method of recovering nitrobenzene from admixture with hydrocarbon oil, which comprises contacting the nitrobenzene and oil With an aliphatic alcohol at a temperature of from about 250 F. to about 400 F., eiecting separation of the oil constituents from the nitrobenzene While maintaining the mixturerat substantially such temperature,'removing the separated oil, and cooling the remaining mixture to separate and recover the nitrobenzene.V

8. The method of recovering nitrobenzene from admixture with hydrocarbon oil, which comprises contactingthe nitrobenzene-oil mixture with at least one solvent from the group consisting of glycols and diluted monohydric a1iphatic alcohols, at a temperature of from about 300 F. to about 350o F., eiecting separation of the oil constituents from the nitrobenzene While maintaining the mixture at substantially such temperature, removing the separated oil, and Cooling the remaining mixture to a temperature of from about 60 F. to about 150 F. to separate oilfcompcnents and Ya major quantity of nitro-r benzene, the'steps which comprise contacting at least Yone of sai'dphases With an aliphatic alcohol atfa temperature of from about 250 F. to abouti 350 F.,reffecting lseparation ofY oil constituents from the, nitrobenzene-alcohol mixture at such temperatures', removing the separated oil, cooling the Vnitrobenzene-alcohol mixture to atemperature less than substantially 150 F. to effect separation of the nitrobenzene from the alcohol,v removing the separated nitrobenzene and recirculating at least a portion thereof to the hydrocarbon oil extraction system.

10. The method of recovering a nitrated aromatic hydrocarbon from admixture with hydrocarbon oil, which comprises contacting said ad-A mixture With a solvent for said nitrated aromatic hydrocarbon at a temperature such hat the nitrated aromatic hydrocarbon is extracted to ajsubstantial extent'from the oil, separating oil from the solution of the nitrated aromatic hydrocarbon and solvent, and cooling said solution to separate and recover the nitrated aromatic hydrocarbon.

11. The method of recovering a nitrated aro-V matic hydrocarbon from admixture with hydrocarbon oil, which comprises contacting said admixture, .at a temperature such that the nitrated aromatic hydrocarbon is extracted to a substantial extent from the oil, with a solvent, Which, at said temperature, has substantial solvent power for said nitrated aromatic hydrocarbon but not for oil, separating oil from the solution of the nitrated aromatic hydrocarbon in said solvent, and cooling said solution to separate and recover the nitrated aromatic hydrocarbon.

EUGENE R. BROWNSCOMBE. SEYMOUR.' W. FERRIS. 

